Synthesis and Use of New Substituted 1,3,5-Hexatrienes in Studying Thermally Induced 6π-Electrocyclizations

Cross-Coupling Reactions of Double or Triple Electrophilic Templates for Alkene Synthesis

This short review summarizes the latest advances in the cross-coupling reactions of double and triple electrophilic templates bearing halogen atoms and an activated C–O bond. Reactions involving the formation of a C–C bond as part of di-, tri-, and tetrasubstituted double bond systems are highlighted.

1 Introduction

2 Cross-Coupling Reactions of Halovinyl Tosylates

3 Cross-Coupling Reactions of Halovinyl Triflates

4 Cross-Coupling Reactions of Halovinyl Phosphates

5 Cross-Coupling Reactions of Halovinyl Esters

6 Conclusion

Transition-Metal Catalysis of Triene 6π Electrocyclization: The π-Complexation Strategy Realized

Triene 6π electrocyclization, wherein a conjugated triene undergoes a concerted stereospecific cycloisomerization to a cyclohexadiene, is a reaction of great historical and practical significance. In order to circumvent limitations imposed by the normally harsh reaction conditions, chemists have long sought to develop catalytic variants based upon the activating power of metal-alkene coordination. Herein, we demonstrate the first successful implementation of such a strategy by utilizing [(C₅ H₅ )Ru(NCMe)₃ ]PF₆ as a precatalyst for the disrotatory 6π electrocyclization of highly substituted trienes that are resistant to thermal cyclization. Mechanistic and computational studies implicate hexahapto transition-metal coordination as responsible for lowering the energetic barrier to ring closure. This work establishes a foundation for the development of new catalysts for stereoselective electrocyclizations.

A metal-free aromative cascade for the synthesis of diverse heterocycles

A metal-free aromative cascade has been developed for the synthesis of diverse heterocycles from readily accessible hydroxy/aminochalcones and acid/alkyl halides. The cascade being by a base-mediated intramolecular aldol cyclization/dehydration sequence to provide a triene, which sets the stage for a 6π-electrocyclization/oxidative aromatization to access diverse heterocyclic scaffolds.

The 6π-azaelectrocyclization of azatrienes. Synthetic applications in natural products, bioactive heterocycles, and related fields

Covering: 2006 to 2018 The application of the 6π-azaelectrocyclization of azatrienes as a key strategy for the synthesis of natural products, their analogs and related bioactive or biomedically-relevant compounds (from 2006 to date) is comprehensively reviewed. Details about reaction optimization studies, relevant reaction mechanisms and conditions are also discussed.

An efficient and practical entry to 2-amido-dienes and 3-amido-trienes from allenamides through stereoselective 1,3-hydrogen shifts

Preparations of de novo acyclic 2-amido-dienes and 3-amido-trienes through 1,3-hydrogen shifts from allenamides are described. These 1,3-hydrogen shifts could be achieved thermally or they could be promoted by the use of Brønsted acids. Under either condition, these processes are highly regioselective in favour of the α-position, and highly stereoselective in favour of the E-configuration. In addition, 6π-electron electrocyclic ring-closure could be carried out with 3-amido-trienes to afford cyclic 2-amido-dienes, and such electrocyclic ring-closure could be rendered in tandem with the 1,3-hydrogen shift.

Stereoselective 6π-electron electrocyclic ring closures of 2-halo-amidotrienes via a remote 1,6-asymmetric induction

A diastereoselective 6π-electrocyclic ring closure employing halogen-substituted 3-amidotrienes via a 1,6-remote asymmetric induction is described. This new asymmetric manifold for pericyclic ring closure further underscores the significance of the allenamide chemistry.

Torquoselective ring closures of chiral amido trienes derived from allenamides. A tandem allene isomerization-pericyclic ring-closure-intramolecular Diels-Alder cycloaddition

A new torquoselective ring-closure of chiral amide-substituted 1,3,5-hexatrienes and its application in tandem with [4 + 2] cycloaddition are described. The trienes were derived via either a 1,3-H or 1,3-H-1,7-H shift of alpha-substituted allenamides, and the entire sequence through the [4 + 2] cycloaddition could be in tandem from allenamides.

Regio- and stereoselective isomerizations of allenamides: synthesis of 2-amido-dienes and their tandem isomerization-electrocyclic ring-closure

A regio- and stereoselective isomerization of allenamides is described, leading to preparations of de novo 2-amido-dienes and a tandem isomerization-6pi-electron electrocyclic ring-closure.